An on-load tap changer with semiconductor switching elements that is constructed as a hybrid IGBT switch is known from WO 2001/022447. The on-load tap changer described there operates according to the principle of a continuous load switch, in which it is possible to dispense with a force store. As hybrid switch, it has a mechanical part and an electrical part. The mechanical part, which is the actual subject of WO 2001/022447, has mechanical switch contacts; the central part is a movable slide contact that is moved by means of a motor drive along a contact guide rail connected with the neutral point and in that case connects stationary contact elements. The actual load changeover itself is carried out by two IGBTs each with four diodes in rectifier-circuit arrangement. This known concept of a hybrid switch is mechanically complicated and demanding in order to ensure the necessary load changeover precisely at the zero transition of the load current.
A further IBGT switching device in which the taps of the regulating winding of a power transformer are connected with a common load shunt by way of a series connection of two IGBTs is known from WO 1997/005536 [U.S. Pat. No. 5,969,511]. This known switching device operates according to the principle of pulse width modulation; in that case, limitation of the circular current takes place by the transient reactive reactance (TER) of the tapped winding. This known switching arrangement and the underlying switching principle require specific adaptation of the on-load tap changer to the respective tapped transformer that is to be connected. In other words, tapped transformer and on-load tap changer are matched to one another and interact electrically. This known switching device is thus not able to be produced as a separate, universally usable apparatus.
Finally, various switching arrangements for an on-load tap changer, which include varistors connected in various ways, are known from GB 2424766. In one form of embodiment, varistors are connected parallel to the respective switching elements and serve for voltage dividing.